Electron-emitting device, electron source and image-forming apparatus, and method for manufacturing electron emitting device

ABSTRACT

To provide an electron-emitting device, an electron source, an image-forming apparatus, and a method for manufacturing the electron-emitting device whereby it is possible to reduce a device capacity and a driving voltage, to improve the efficiency of emitting electrons, and to obtain high-resolution beam. The extracting electrode and the cathode electrode are provided on an insulating substrate, a layer having growth selectivity of fibrous carbon is formed on the cathode electrode, and the fibrous carbon is grown via catalyst particles formed on the layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron-emitting device, anelectron source having the electron emitting device, and animage-forming apparatus for using and applying the electron source, andto a display apparatus for broadcast on television, a display apparatusfor a TV conference system, a computer, and so on, and an image-formingapparatus used as an optical printer, which is composed of aphotosensitive drum and the like. The present invention further relatesto a method for manufacturing an electron-emitting device.

2. Related Background Art

Development of an image-forming apparatus using an electron-emittingdevice has been pursued in recent years.

A field emission (FE type) electron-emitting device has become a focusof attention as one of cold electron sources. The field emissionelectron-emitting device applies a strong electric field of 10⁶ V/cm ormore on metal and emits an electron from a metal surface.

If a cold electron source of FE type is put into practical use, alow-profile emissive type image display apparatus can be achieved,thereby saving power consumption with light weight.

As an example of an vertical type FE, FIG. 13 shows an emitter 135formed into a circular cone or a quadrangular pyramid in substantially aperpendicular direction from a substrate 131. For example, an verticaltype FE has been known, which is (hereinafter, referred to as a spinttype) in C. A. Spindt, “Physical Properties of thin-film field emissioncathodes with molybdenium cones”, J. Appl. Phys., 47,5248 (1967) and soon.

Meanwhile, FIG. 14 shows the configuration of a lateral type FE.Besides, in FIG. 14, reference numeral 141 denotes a substrate,reference numeral 142 denotes an emitter electrode, reference numeral143 denotes an insulating layer, reference numeral 145 denotes anemitter, reference numeral 146 denotes an anode, and reference numeral147 denotes the shape of an electron beam emitted to the anode. Theemitter 145 having a pointed end and a gate electrode 144 are disposedin parallel on the substrate, and a collector (anode electrode) isformed above the substrate having the gate electrode and the emitterelectrode thereon (refer to U.S. Pat. Nos. 4,728,851, 4,904,895 and thelike).

Further, as an example of an electron-emitting device using fibrouscarbon, Japanese Patent Application Laid-Open No. 8-115652 discloses theconfiguration in which thermal decomposition is performed on a finecatalyst metal by using organic compound gas to deposit fibrous carbonin a fine gap.

As a conductive layer for a carbon nanotube, Japanese Patent ApplicationLaid-Open No. 11-194134 and EP0913508A2 disclose a metal layer made oftitanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), molybdenum(Mo). Moreover, Japanese Patent Application Laid-Open No. 11-139815discloses that Si is used as a conductive substrate.

In a conventional image-forming apparatus using an FE electron source,an electron beam spot (hereinafter, referred to as a beam diameter) isobtained according to a distance H between an electron source andphosphor and a driving voltage Vf of an anode voltage Va and an element.The beam diameter is about a submillimeter and its resolution has beensufficient for an image-forming apparatus.

However, as for an image-forming apparatus, a higher resolution has beendemanded in recent years.

Furthermore, as the number of display pixels increases, powerconsumption rises due to a device capacity of an electron-emittingdevice when driving. Thus, a reduced device capacity, a reduced drivingvoltage, and an increased electron emission efficiency of anelectron-emitting device have been demanded.

SUMMARY OF THE INVENTION

Such a related art has the following problems.

Since the above-mentioned spint type is configured such that the gate islaminated on the substrate, a parasitic capacity is formed between alarge gate capacity and a number of emitters. Further, the spint typehas a high driving voltage of several tens volts and a capacitive powerconsumption is large. Moreover, a beam spreads at an anode.

Although the horizontal FE can reduce a capacity of an element, avoltage of several hundreds of volts is required for driving because ofa large distance between the emitter and the gate, resulting in a largedriving device. Further, a beam spreads at the anode.

Although beam focusing means may be provided on the spint-type andlateral FE electron-emitting device, problems arise such as acomplicated manufacturing scheme, an increased device area, and areduced electron-emission efficiency.

The present invention is devised to solve the above problems. The objectis to provide an electron-emitting device, an electron source, animage-forming apparatus, and a scheme of manufacturing anelectron-emitting device that can reduce an device capacity and adriving voltage, improve the electron emission efficiency, and obtain ahigh-resolution beam.

An electron-emitting device of the present invention devised to attainthe above object includes fiber comprising carbon as a main ingredient,a layer made of oxide of a material selected from Ti, Zr, Nb, and Al ora layer composed of an oxide semiconductor made of a material selectedfrom Ti, Zr, and Nb. The fiber comprising carbon as a main ingredient isdisposed on the layer and has Pd partially therein.

Further, the electron-emitting device of the present invention that isdevised to attain the above-mentioned object includes first and secondelectrodes disposed with an interval on a substrate surface, a pluralityof fibers that is electrically connected to the first electrode andcomprising carbon as a main ingredient, and means for applying apotential higher than the first electrode to the second electrode,characterized in that the ends of the plurality of fibers, whichcomprising carbon as a main ingredient, are higher than the surface ofthe second electrode from the substrate surface, and a layer made ofoxide composed of a material selected from Ti, Zr, Nb, and Al or a layermade of oxide semiconductor composed of a material selected from Ti, Zr,and Nb is disposed between the first electrode and the plurality offibers comprising carbon as a main ingredient.

Moreover, the electron-emitting device of the present invention that isdevised to attain the above-mentioned object includes a fiber comprisingcarbon as a main ingredient, and a layer made of oxide composed of amaterial selected from Ti, Zr, Nb, and Al or a layer made of oxidesemiconductor composed of a material selected from Ti, Zr, and Nb, andthe fiber comprising carbon as a main ingredient is disposed on thelayer, and the fiber comprising carbon as a main ingredient has aplurality of layered graphenes.

Also, a method for manufacturing the electron-emitting device includingfiber comprising carbon as a main ingredient that is devised to attainthe above-mentioned object includes a step of disposing on a substrate alayer made of oxide composed of a material selected from Ti, Zr, Nb, andAl or a layer made of oxide semiconductor composed of a materialselected from Ti, Zr, and Nb; a step of disposing catalyst particles onthe layer; and a step of heating the substrate having the catalystparticles thereon in an atmosphere containing a carbon compound.

Furthermore, the present invention is characterized by an electronsource using the above electron-emitting device and the image-formingapparatus. Besides, the present invention is characterized by anelectron source using a method for manufacturing the aboveelectron-emitting device and a method for manufacturing theimage-forming apparatus.

According to the present invention, fiber comprising carbon as a mainingredient is provided on the layer containing a material having growthselectivity. Thus, the fiber comprising carbon as a main ingredient canobtain stable electrical connection and an electron-emitting devicehaving excellent characteristics can be formed with a simple process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic structural diagrams showing anelectron-emitting device according to Example 1 of the presentinvention;

FIGS. 2A and 2B are schematic structural diagrams showing anelectron-emitting device according to Example 2 of the presentinvention;

FIGS. 3A and 3B are schematic structural diagrams showing anelectron-emitting device according to Example 3 of the presentinvention;

FIGS. 4A and 4B are schematic structural diagrams showing anelectron-emitting device according to Example 4 of the presentinvention;

FIGS. 5A, 5B, 5C, 5D and 5E are diagrams showing a manufacturing processof the electron-emitting device according to Example 1 of the presentinvention;

FIG. 6 is a schematic diagram showing that an electron-emitting deviceis operated according to an example of the present invention;

FIG. 7 is a schematic diagram showing operating characteristics of theelectron-emitting device according to an example of the presentinvention;

FIG. 8 is a schematic structural diagram showing a passive-matrixcircuit of an electron source according to an example of the presentinvention;

FIG. 9 is a schematic structural diagram showing a display panel of animage-forming apparatus according to an example of the presentinvention;

FIG. 10 is a schematic structural diagram showing a circuitconfiguration of the image-forming apparatus according to an example ofthe present invention;

FIG. 11 is a schematic diagram showing the configuration of a carbonnanotube;

FIG. 12 is a schematic diagram showing the configuration of a graphitenanofiber;

FIG. 13 is a schematic perspective view showing a conventional verticalFE; and

FIG. 14 is a schematic perspective view showing conventional horizontalFE.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to figures, the following will discuss the detail of thepreferred embodiments of the present invention. However, regarding thedimensions, materials, shapes, and relative positions of membersdescribed in the embodiments, the present invention is not limitedunless otherwise specified.

The inventor studied a material which forms a fine (on the order ofseveral nm) nuclear (catalyst particle) by using a catalyst and makeselectrical connection in stable manner with fibrous carbon growing fromthe nuclear by pyrolysis.

As a result, the inventor found that a material which allows a fibrouscarbon to grow via a catalyst and provides an electrical connection isTi, Zr, Nb, And Al, and that a partially (an interface making contactwith the fibrous carbon or catalyst) oxidized material or an oxidesemiconductor of Ti, Zr, and Nb can be suitably used.

And then, as a result of another detailed study, the inventor found thatfibrous carbon can be generated at a position having a catalyst particlewith good reproducibility by using a member having a catalyst particle(particularly Pd) on an oxide of a material selected from Ti, Zr, andAl.

Further, the inventor simultaneously found that a material not allowingfibrous carbon to grow or a material growing slowly is the same kind ofmaterial as Ta, Cr, Ag, Pt and a catalyst material.

Growth of the fibrous carbon on these materials is allowed on a layeredstructure as well. For example, Cr is entirely formed on a substrate, asmall area of titanium oxide is formed thereon, and the surface of thesubstrate is entirely coated with palladium oxide. Fibrous carbon isselectively formed only on titanium oxide.

The following will discuss an electron-emitting device, an electronsource, and an image-forming apparatus of the present invention that usethe above-mentioned technique for forming fibrous carbon at apredetermined position with good reproducibility in comparison with therelated art.

In general, an operating voltage Vf of an FE device is determined by anelectric field at the end of an emitter and a current density ofelectron emission current. The electric field is derived by Poissonequation and the current density is computed by a relationship equationreferred to as Fowler-Nordheim equation while a work function of theelectric field and the emitter is used as a parameter.

Further, an electric field required for electron emission becomes largeas a distance d between the end of the emitter and the gate electrodebecomes small or a radius r of the end of the emitter becomes small.

Meanwhile, regarding an electron beam obtained on an anode in the xdirection, a maximum Xd (e.g., a maximum throw from the center of theconical beam 137 shown in FIG. 13) is proportional to (Vf/Va) accordingto a simple computing, wherein Va is a voltage applied to an anode.

As indicated by the above relationship, an increase in Vf raises a beamdiameter.

Moreover, according to the above-configuration, it is necessary tominimize a distance d and a curvature r to reduce Vf.

Referring to FIGS. 13 and 14, the shape of beam of the conventionalconfiguration will be described. Here, in the figures, referencenumerals 131 and 141 denote substrates, reference numerals 132 and 142denote emitter electrodes, reference numerals 133 and 143 denoteinsulating layers, reference numeral 135 and 145 denote emitters,reference numerals 136 and 146 denote anodes, and reference numerals 137and 147 denote the shapes of electron beam emitted on the anodes as thecommon numerals.

In the case of the above-mentioned spint type, as shown in FIG. 13, whena voltage Vf is applied between the emitter 135 and the gate 134, anelectric field is enhanced on the projecting end of the emitter 135 andan electron is emitted from around the end of the conical emitter to avacuum.

An electric field on the end of the emitter 135 is formed with a limitedarea according to the shape of the emitter 135. Hence, an electron isdrawn from the limited area of the end of the emitter 135 in aperpendicular direction to a direction of the electric field.

At this moment, electrons with a variety of angles are emitted. Anelectron having a large angle component is drawn to a direction of thegate. When a circular gate 134 is formed, the distribution of electronson the anode 136 is formed as the beam shape 137, which is substantiallycircular as shown in FIG. 13.

Namely, the obtained shape of beam is closely associated with the shapeof the gate and a distance between the gate and the emitter.

In the case of a lateral type FE (FIG. 14) in which extractiondirections of electrons are aligned, an extremely strong electric field(lateral electric field) is generated between the emitter 145 and thegate 144 substantially in parallel with the surface of the substrate141. Consequently, as for electrons emitted from the emitter 145, someelectrons 149 are drawn into a vacuum, and the other electrons are takeninto the gate electrode 144.

In the case of the configuration shown in FIG. 14, an electric-fieldvector for emitting electrons (an electric field from the emitter 145 tothe gate 144) is different in orientation from a direction of anelectric-field vector provided toward the anode (anode electrode) 146.Therefore, emitted electrons form a large distribution (beam spot) ofelectrons on the anode 146.

Here, an electric field where electrons are drawn from the emitter 145(referred to as “lateral electric field” for convenience, and theenhancement effect of the electric field according to the shape of theemitter is ignored) and an electric field toward the anode (referred toas “vertical electric field”) will be considered.

Besides, in the configurations of FIGS. 13 and 14, the “lateral electricfield” is also referred to as “electric field substantially in parallelwith the surface of the substrate 131 (141)”. Moreover, particularly inthe configuration of FIG. 14, the electric field is also referred to as“electric field in an opposing direction of the gate 144 and the emitter145”.

Also, in the configurations of FIGS. 13 and 14, the “vertical electricfield” can also be referred to as the “electric field substantiallyperpendicular to the surface of the substrate 131 (141)” or the“electric field in an opposing direction of the substrate 131 (141) andthe anode 136 (146)”.

As described above, an electron emitted from the emitter 145 is firstlydrawn by a lateral electric field and is emitted toward the gate 144.And then, the electron is drawn upward by the vertical electric fieldand reaches the anode 146.

At this moment, an intensity ratio of strengths of the lateral electricfield and the vertical electric field and relative positions of electronemission point are important.

When the lateral electric field is stronger than the vertical electricfield by an order of magnitude, most of electrons emitted from theemitter gradually change their trajectories due to radial potentialformed by the lateral electric field, and the electrons travel towardthe gate. Some electrons colliding with the gate are emitted again byscattering. After emission, the electrons are repeatedly scattered whilespreading on the gate by repeatedly traveling on oval trajectories untilthe electrons are captured by the vertical electric field. At thismoment, the number of emitted electrons decreases. And then, whenscattered electrons travel beyond an equipotential line (may be referredto as “stagnation point”) produced by the gate potential, the electronsare drawn upward by the vertical electric field for the first time.

When the lateral electric field and the vertical electric field areapproximately equal in strength to each other, although extractedelectrons change its trajectories due to a radial potential, theconstraint of an electric field is eased. Thus, it is possible toproduce an electron trajectory captured by the vertical electric fieldwithout collision with the gate 144.

It was found that when the lateral electric field and electric field areapproximately equal in strength to each other, an electron emissionpoint from the emitter 145 is gradually shifted upward from a planeincluding the gate 144 to a plane including the anode 146 (see FIG. 6).In this case, emitted electrons do not collide with the gate 144 at allbut can travel on trajectories to be captured by the vertical electricfield.

Further, as a result of the study of an electric field ratio, it isfound that if a distance is d between the gate electrode 144 and the endof the emitter electrode 145, a potential difference (potentialdifference between the gate electrode and the emitter electrode) is V1when the device is driven, a distance is H between the plate (anode) andthe substrate (device), and a potential difference is V2 between theplate (anode) and a cathode (emitting electrode), when the lateralelectric field is 50-time larger than the vertical electric field,trajectories are drawn such that extracted electrons are collided withthe gate.

Moreover, the inventor found a height s causing substantially noscattering on the gate electrode 2 (height s being defined as a distancebetween a plane including a part of the surface of the gate electrode 2and being disposed substantially in parallel with the surface of thesubstrate 1, and a plane including the surface of an electron-emittingmember 4 and being disposed substantially in parallel with the surfaceof the substrate 1 (see FIG. 6)). The height s is dependent upon a ratioof the vertical electric field and a lateral electric field (e.g,. thestrength of the vertical electric field vs. the strength of the lateralelectric field). The height s needs to be lower as the vertical electricfields is lower, and the height s needs to be higher as the lateralelectric field is larger.

A practical fabrication range of the height s is not less than 10 nm normore than 10 μm.

In the conventional configuration shown in FIG. 14, the gate 144 and theemitter (142, 145) are provided on the same surface at an equal height.Additionally, since the lateral electric field is stronger than thevertical electric field by an order of magnitude, the amount ofextracted electrons into a vacuum is prone to decrease because of thecollision with the gate.

Furthermore, in the conventional configuration, the thickness and widthof the gate electrode and the relative position of the gate, theemitter, and the anode were determined for the purpose of enhancing theintensity of the lateral electric field. Hence, the distribution spreadsregarding electrons obtained on the anode.

As described above, in order to reduce the distribution of electronsreaching the anode 146, the following points need to be considered. 1)Reducing a driving voltage (Vf), 2) aligning the extraction directionsof electrons, 3) when scattering is found on the trajectories ofelectrons and on the gate, 4) a electron-scattering mechanism(particularly elastic scattering).

According to the electron-emitting device using fibrous carbon of thepresent invention, a fine distribution of electrons emitted on the anodeelectrode is compatible with increasing the efficiency of electronemission (reducing emitted electrons absorbed by the gate electrode).

The following will discuss the configuration of the electron-emittingdevice of the present invention.

FIG. 1A is a plan view schematically showing an example of theelectron-emitting device of the present invention. FIG. 1B is a sectionview taken along line 1B—1B shown in FIG. 1A. FIG. 6 is a section viewschematically showing that an electron-emitting apparatus of the presentinvention is driven in which an anode electrode is disposed above theelectron-emitting device of the present invention.

In FIGS. 1 and 6, reference numeral 1 denotes an insulating substrate,reference numeral 2 denotes a extracting electrode (referred to as a“gate electrode” or a “second electrode”), reference numeral 3 denotes anegative electrode (also referred to as a “cathode electrode” or a“first electrode”), reference numeral 4 denotes an electron-emittingmaterial (also referred to as an “electron-emitting member” or an“emitter material”) disposed on the negative electrode 3, and referencenumeral 5 denotes a layer for selectively growing fibrous carbon that ismade of oxide of a material selected form Ti, Zr, Nb, and Al. Thefibrous carbon for forming the electron-emitting material 4 iselectrically connected to the electrode 3.

Besides, when the layer 5 for selectively growing fibrous carbon isformed with a large thickness, since the layer 5 is made of oxide,electrical connection between fibrous carbon and the electrode 3 may beweakened. Therefore, in order to sufficiently obtain electricalconnection between fibrous carbon and the electrode 3, at least thesurface of the layer 5 for forming fibrous carbon is composed of oxideof a material selected from Ti, Zr, Nb, and Al, and the other parts aremade of metal.

As shown in FIGS. 1 and 6, in the electron-emitting apparatus of thepresent invention, the plane including the surface of theelectron-emitting member 4 substantially in parallel with the surface ofthe substrate 1 is disposed farther from the surface of the substratethan the plane including a part of the surface of the gate electrode 2substantially in parallel with the surface of the substrate 1. In otherwords, in the electron-emitting apparatus of the present invention, theplane including a part of the surface of the electron-emitting member 4in parallel with the surface of the substrate 1 is disposed between ananode electrode 61 and the plane including a part of the extractingelectrode 2 substantially in parallel with the surface of the substrate.With this configuration, it is possible to reduce electrons captured bythe gate electrode and reduce spot diameter of an electron beam emittedonto the anode electrode.

Besides, in the electron-emitting device of the present invention, theelectron-emitting member 4 is disposed at a height s (defined by adistance between the plane including a part of the surface of the gateelectrode 2 substantially in parallel with the surface of the substrate1 and the plane including the surface of the electron-emitting member 4substantially in parallel with the surface of the substrate 1), wheresubstantially no scattering occurs on the gate electrode 2.

The height s is dependent upon a ratio of the vertical electric fieldand the lateral electric field (vertical electric fieldintensity/lateral electric field intensity). The height needs to belower as a ratio of the vertical electric field and a lateral electricfield is lower, and the height needs to be higher as the lateralelectric field is larger. The practical range of the height s is notless than 10 nm nor more than 10 μm.

Further, in the electron-emitting apparatus of the present invention,according to the configuration of FIG. 6, when a distance is d betweenthe cathode 3 and the gate electrode 2, a potential difference (voltagebetween the cathode 3 and the electrode 2) is Vf when theelectron-emitting device is driven, a distance is H between the surfaceof the substrate 1 and the anode electrode 61, and a potentialdifference is Va between the anode electrode 61 and the cathodeelectrode 3, an electric field when driving (lateral electric field):El=Vf/d is set to be not less than 1 times nor more than 50 timesstronger than the electric field between the anode 61 and the cathode 3(vertical electric field).

Therefore, it is possible to eliminate a ratio of electrons collidingwith the gate electrode after being emitted from the cathode electrode3. Consequently, there are provided the electron-emitting device and theelectron-emitting apparatus with the extremely small spread of theemitted electron beam and with high electron emission efficiency.

Additionally, the “lateral electric field” of the present invention isalso referred to as the “electric field substantially in parallel withthe surface of the substrate 1” or the “electric field in an opposingdirection of the gate electrode 2 and the cathode electrode 3”. Further,the “vertical electric field” of the present invention is also referredto as the “electric field substantially in a perpendicular direction tothe surface of the substrate 1” or the “electric field in an opposingdirection of the substrate 1 and the anode electrode 61”

As the insulating substrate 1, it is possible to adopt a substrate whichhas a sufficiently cleaned surface and is made of quartz glass, glass inwhich the content of impurity such as Na is reduced and is partiallysubstituted by K or the like, soda lime glass, a layered body havingSiO₂ layered on the silicon substrate and the like by sputtering and thelike, or an insulating substrate made of ceramic including aluminum.

The extracting electrode (gate electrode) 2 and the cathode electrode 3are conductive and are formed by a typical vacuum film-forming techniquesuch as vapor deposition and sputtering scheme or by photo lithographytechnique. The electrodes (2, 3) are made of a material suitablyselected from carbon, metal, metal nitride, metal carbide, metal boride,a semiconductor, and a semiconductor-metal compound, preferably from aheat-resistant material such as carbon, metal, metal nitride and metalcarbide. The electrodes has a thickness of several tens nm to severaltens μm.

Besides, when a potential drop may occur due to a small thickness of theelectrode or when the device is used in a matrix, a low-resistancewiring metallic material may be used as necessary. However, the usage islimited to a part not being associated with electron emission.

Moreover, in the above example, the cathode electrode 3 and the layer 5for selectively growing fibrous carbon are composed of differentmembers. For example, the layer 5 for selectively growing fibrous carbonmay be formed by allowing an electrode made of a material selected fromTi, Zr, Nb, and Al to constitute the cathode electrode 3 and oxidizingthe surface.

The electron-emitting device of the present invention is made of fibrouscarbon as the emitter (electron-emitting member) 4. Additionally,“fibrous carbon” of the present invention is also referred to as “acolumnar substance comprising carbon as a main component” or “a linearsubstance comprising carbon as a main component”. Further, “fibrouscarbon” of the present invention is also referred to as “fibercomprising carbon as a main component”. Furthermore, “fibrous carbon” ofthe present invention specifically includes carbon nanotube, graphitenanofiber, and amorphous carbon fiber. Graphite nanofiber is the mostpreferable as the electron-emitting member 4.

As described above, regarding a distance and a driving voltage betweenthe extracting electrode 2 and the cathode electrode 3, when comparisonis made between an electron-emitting electric field (lateral electricfield) of a used cathode material and the vertical electric fieldrequired for forming an image, it is preferable to set anelectron-emitting electric field at about 1 to 50 times larger than avertical electric field.

When a light emitting member such as a phosphor or the like is disposedon the positive electrode (anode electrode), a necessary verticalelectric field is preferable in the range of not less than 10⁻¹ V/μm normore than 10 V/μm. For example, when a distance is 2 mm between apositive electrode (anode electrode) and a cathode electrode and 10 kVis applied therebetween, the vertical electric field is 5V/μm then. Inthis case, an emitter material (electron-emitting member) 4 to be usedhas an electron-emitting electric field of larger than 5 V/μm. Adistance and a driving voltage thereof are determined so as tocorrespond to a selected electron-emitting electric field.

The above-mentioned fibrous carbon is preferable as a material havingsuch a threshold electric field of several V/μm.

FIGS. 11 and 12 show examples of configurations of fibrous carbonsuitable for the present invention. In each of the schematic drawing,the left shows a configuration found at an optical microscope level (to1000 times), the center shows a configuration found at a scanningelectron microscope (SEM) level (to 30000 times), and the right shows aconfiguration of carbon found at a transmission electron microscope(TEM) level (to million times).

As shown in FIG. 11, graphen formed into a cylinder (cylinder having amultiplex structure is referred to as a multi-wall nanotube) is referredto as a carbon nanotube. Particularly when a tube end is opened, athreshold value is lowered to the minimum.

FIG. 12 shows fibrous carbon may be produced at a relatively lowtemperature. Fibrous carbon having such a configuration is composed of agraphen layered body (thus, it may be referred to as “graphitenanofiber” and has an amorphous structure whose ratio is increased withtemperature). To be specific, graphite nanofiber is a fibrous substancein which graphens are layered (laminated) in the longitudinal directionthereof in the axis direction of the fiber. In other words, as shown inFIG. 12, graphite nanofiber is a fibrous substances in which a pluralityof graphens are aranged and layered (laminated) so as not to be parallelto the axis of fiber.

Meanwhile, carbon nanotube is a fibrous substance in which graphens arearranged (in cylindrical shape) around the longitudinal direction (axialdirection of fiber). In other words, it is a fibrous substance in whichgraphens are arranged substantially in parallel to the axis of thefiber.

Besides, a single surface of graphite is referred to as “graphen” or“graphen sheet”. To be specific, graphite is a lamination in whichcarbon planes, each of which is a spread of regular hexagons consistingof covalent bouds of carbon atoms in sp² hybrid, are layered atintervals of distance of 3.354 Å. Each of the carbon planes is referredto as “graphen” or “graphen sheet”.

Each fibrous carbon has an electron-emitting threshold value at about 1to 10 V/μm and is very preferable as a material of the emitter(electron-emitting member) 4 of the present invention.

Particularly, regarding an electron-emitting device using graphitenanofiber, it is possible to achieve an electron-emitting device, whichemits an electron with a low-electric field, obtains a large emittingcurrent, is manufactured with ease, and has stable electron-emittingcharacteristics. The configuration of the device is not limited to thatof the present invention. For example, an electron-emitting device canbe formed by using graphite nanofiber as an emitter and preparing anelectrode for controlling electrons emitted from the emitter. Further, alight-emitting apparatus such as a lamp can be formed by using a lightemitting member which emits light under irradiation of electrons emittedfrom graphite nanofiber. Furthermore, a plurality of electron-emittingdevices using the graphite nanofiber is arranged and an anode electrodehaving a light emitting member such as a phosphor is prepared to form animage display apparatus such as a display. In an electron-emittingapparatus, a light-emitting apparatus, and an image display apparatusthat use graphite nanofiber, it is possible to emit electrons in astable manner without keeping the inside at an ultrahigh vacuum asrequired in the conventional electron-emitting device, and it ispossible to obtain a large amount of emitting electrons in a lowelectric field. Hence, it is possible to manufacture a reliableapparatus with great ease.

The above fibrous carbon can be formed by using a catalyst (material forencouraging the deposition of carbon) to decompose hydrocarbon. Carbonnanotube and graphite nanofiber are different from each other in a typeof a catalyst and a decomposing temperature.

As the catalyst material, it is possible to adopt Fe, Co, Pd, and Ni oran alloy of a material selected from the above as a nuclear for formingfibrous carbon.

Particularly, Pd can form graphite nanofiber at a low temperature (at400° C. or higher). Meanwhile, when Fe or Co is used as a catalyst, aforming temperature of carbon nanotube needs to be 800° C. or higher. Agraphite nanofiber material can be produced at a low temperature when Pdis used. Hence, Pd is preferable in view of the influence of the othermembers and the manufacturing cost.

Moreover, Pd makes it possible to use palladium oxide as a nuclearforming material by using a characteristic of oxide reduced by hydrogenat a low temperature (room temperature).

When hydrogen is reduced in palladium oxide, it is possible to form aninitial aggregation nuclear at a relatively low temperature (200° C. orlower) without using thermal aggregation of a metallic thin film thathas been conventionally used as a typical nuclear forming scheme orgeneration and evaporation of ultra-fine particles that may causeexplosion.

As the carbon hydrogen gas, for example, it is possible to adopthydrocarbon gas such as ethylene, methane, propane, and propylene ororganic solvent vapor such as ethanol and acetone.

Additionally, as a material as fibrous carbon, it is possible to adopt amaterial such as CO and CO₂ as well as the hydrocarbon gas.

As a material of the layer 5 shown in FIGS. 1 and 6, as described above,it is possible to adopt an oxide of a material selected from Ti, Zr, Nb,and Al that has growth selectivity of fibrous carbon or an oxidesemiconductor made of a material selected from Ti, Zr, and Nb.

A stoichiometry oxide of the Ti, Zr, Nb is an insulator. A weak oxide ora suboxide has a large number defects therein to form a semiconductorhaving a loss of oxygen and so on.

However, Al does not form an oxide film having conductivity. Therefore,when an oxide made of Al is used, it is necessary to use a conductingmechanism, in which electrons perform tunneling on an insulating film,to obtain electrical connection between fibrous carbon and the cathodeelectrode 3, by reducing a thickness of an oxide film layer formed on asurface of Al.

In the present embodiment, Pd is baked for several tens minutes at about300° C. on an oxide made of a material selected from Ti, Zr, Nb, and Al.Thus, palladium oxide is formed. At this moment, Ti, Zr, Nb, or Al isoxidized. The above baking temperature and time does not entirelyoxidize the layer 5 but only the surface thereof although depending onthe thickness of the initially deposited layer 5. Further, as describedabove, due to semiconductor characteristics, as a result, the layer 5formed in the above manner can have conductivity.

Further, since the surface of the layer 5, on which catalyst particlesmade of a material such as Pd, is made of oxide, it is possible tosuppress reaction of the material of the layer 5 and the catalystparticles when fibrous carbon is grown. Consequently, it is possible togrow fibrous carbon with stability and a high density.

Thus, as shown in FIGS. 1A and 1B, a plurality of fibrous carbon isgrown on the layer 5 to form the electron-emitting member (emitter) 4.

Regarding the electron-emitting device, the electron-emitting apparatus,and the image-forming apparatus of the present invention, a regionhaving the emitter (electron-emitting member) 4 is hereinafter referredto as an “emitter region” regardless of the presence or the absence ofelectron emission.

An electron emitting portion in the “emitter region” and the generationtherein are described below.

The electron-emitting device having a distance of several μm between thecathode electrode 3 and the extracting electrode 2 is provided in avacuum 60 shown in FIG. 6. A vacuum evacuating device 65 sufficientlyperforms vacuuming to about 10⁻⁴ Pa. As shown in FIG. 6, the surface ofthe positive electrode (anode electrode) 61 is positioned at a height H,which is higher than the surface of the substrate 1 by severalmillimeters, and a potential (voltage Va (several kV)) higher than thecathode electrode 3 and the extraction electrode 2 is applied to theanode electrode 61 by using a voltage source (“second voltage applyingmeans” or “second potential applying means”). In this case, a potentialis applied between the cathode electrode 3 and the anode electrode 61. Avoltage applied to the anode can be also determined according to aground potential. Additionally, the surface of the substrate 1 and thesurface of the positive electrode 61 are disposed substantially inparallel with each other.

In the device, a voltage of about several tens V is applied between thecathode electrode 3 and the extracting electrode 2 as a driving voltageVf by a power supply (not shown, “first voltage applying means” or“first potential applying means”), and measurement is made on a devicecurrent If, which flows between the electrodes 2 and 3, and anelectron-emitting current Ie applied to the anode electrode.

At this moment, equipotential lines 63 are formed as shown in FIG. 6(electric fields (directions of electric fields) are formedsubstantially in parallel with the surface of the substrate 1). It isexpected that the most concentrated point of electric fields is theportion of the electron-emitting member 4 closest to the anode electrodethat is indicated by reference numeral 64 and the point faces a gap. Itis expected that electrons are mainly emitted from a concentrated pointof electric fields of electron-emitting materials disposed around theconcentrated point of electric fields. The device has Ie characteristicsshown in FIG. 7. Namely, Ie rises rapidly from about a half of anapplied voltage, and If (not shown) is similar to Ie in characteristics.A value of If is sufficiently small as compared with Ie.

Next, referring to FIG. 8, the following will discuss an electron sourceand an image-forming apparatus having a plurality of electron-emittingdevices, which are formed according to the above-mentioned mentionedprinciple. In FIG. 8, reference numeral 81 denotes an electron sourcesubstrate, reference numeral 82 denotes X-direction wiring, andreference numeral 83 denotes Y-direction wiring. Reference numeral 84denotes electron-emitting devices and reference numeral denotesconnection.

The X-direction wiring 82 is composed of m wires of Dx1, Dx2, . . . ,and Dxm, each being made of conductive metal and so on formed by ascheme such as vacuum deposition, printing scheme, and sputteringscheme. A material, a thickness and a width of wiring are set asappropriate.

The Y-direction wiring 83 is composed of n wires of Dy1, Dy2, . . . ,and Dyn which are formed in the same manner as the X-direction wiring82.

Between the X-direction wiring 82 having m wires and the Y-directionwiring 83 having n wires, an interlayer insulting film (not shown) isprovided to electrically insulate the wiring (m and n are both positiveintegers).

The interlayer insulating film (not shown) is made of a material such asSiO₂, which is formed by a scheme such as vacuum deposition, printingscheme, and sputtering scheme. The interlayer insulating film is, forexample, formed entirely or partially on the electron source substrate81 having the X-direction wiring 82 formed thereon with a predeterminedpattern. Particularly, a film thickness, a material, and a manufacturingscheme thereof are determined as appropriate to be resistant to apotential difference between the X-direction wiring 82 and theY-direction wiring 83. The X-direction wiring 82 and the Y-directionwiring 83 are each drawn as external terminals.

A pair of electrodes (not shown) constituting the electron-emittingdevice 84 is electrically connected to the m wires of the X-directionwiring 82 and the n wires of the Y-direction wiring 83 via theconnection 85 made of a material such as conductive metal.

Materials of the X-direction wiring 82, the Y-direction wiring 83, theconnection 85, and the pair of device electrodes may be partially ortotally the same or different from each other in their constituentelement. For example, these materials are appropriately selected fromthe materials of the device electrode. When the device electrode and thewiring shares the same materials, wiring connected to the deviceelectrode can be referred to as a device electrode.

Scanning signal applying means (not shown), which applies a scanningsignal for selecting a row of the electron-emitting devices 84 arrangedin X direction, is connected to X-direction wiring 82. Meanwhile,modulating signal generating means (not shown) for modulating eachcolumn of electron-emitting devices 84 in response to an input signal isconnected to the Y-direction wiring 83. A driving voltage applied toeach of the electron-emitting devices is supplied as a differencevoltage between a scanning signal and a modulating signal. Thedifference voltage is applied to the device.

In the above configuration, with passive matrix wiring, it is possibleto select each of the devices and drive them in isolation from eachother.

Referring to FIG. 9, the following will discuss an image-formingapparatus constituted by an electron source using a passive-matrixelectron source. FIG. 9 is a schematic diagram showing an example of adisplay panel of the image-forming apparatus.

In FIG. 9, reference numeral 81 denotes an electron source substrate,reference numeral 91 denotes a rear plate on which the electron sourcesubstrate 81 is fixed, reference numeral 96 denotes a face plate havinga fluorescent film 94, a metal back 95, and so on formed on an innersurface of a glass substrate 93. Reference numeral 92 denotes a supportframe having the rear plate 91 and the face plate 96 connected theretoby using frit glass and the like. Reference numeral 97 denotes anenvelope which is sealed by baking for 10 minutes or more at atemperature range of 400 to 500° C., for example, in an atmosphere, in avacuum, or in nitrogen.

As described above, the envelope 97 is composed of the face plate 96,the support frame 92, and the rear plate 91. The rear plate 91 isprovided mainly for reinforcing the electron source substrate 81. Thus,when the electron source substrate 81 has sufficient strength in itself,the rear plate 91, which is a separate member, is not necessary. Namely,the support frame 92 may be directly sealed onto the electron sourcesubstrate 81 and the envelope 97 may be constituted by the face plate96, the support frame 92, and the electron source substrate 81.Meanwhile, it is possible to form the surrounding member 97 withsufficient strength to an air pressure by providing a support (notshown) referred to as a spacer between the face plate 96 and the rearplate 91.

EXAMPLES

The following will discuss the detail of examples according to thepresent invention.

Example 1

FIG. 1A is a schematic diagram taken from the top of anelectron-emitting device according to Example 1 of the presentinvention. FIG. 1B is a section view taken along line 1B—1B shown inFIG. 1A.

In FIGS. 1A and 1B, reference numeral 1 denotes an insulating substrate,reference numeral 2 denotes a extracting electrode, reference numeral 3denotes a cathode electrode, reference numeral 4 denotes anelectron-emitting member, and reference numeral 5 denotes a layer wherefibrous carbon is grown.

Referring to FIGS. 5A to 5E, the following will discuss the detail of amanufacturing process of the electron-emitting device of this example.

(Step 1)

A quartz substrate is used as the substrate 1. After sufficientcleaning, Ti (not shown) having a thickness of 5 nm and Pt having athickness of 30 nm are evaporated continuously.

Next, in a photolithography process, a resist pattern is formed using apositive photoresist (AZ1500/manufactured by Clariant InternationalLtd.).

Next, dry etching is performed on the Pt layer and the Ti layer using Argas with the patterned photoresist serving as a mask to form theextracting electrode 2 and the cathode electrode 3 that have anelectrode gap (distance) of 5 μm (FIG. 5A).

(Step 2)

Next, Cr is deposited entirely on the substrate 1 with a thickness ofabout 100 nm by EB evaporation.

And then, in a photolithography process, a resist pattern is formedusing a positive photoresist (AZ1500/manufactured by ClariantInternational Ltd.).

Subsequently, the patterned photoresist is used as a mask, a region forcoating electron-emitting materials (100 μm square) is formed on thecathode electrode 3, and Cr on an opening is removed by an etchingsolution made of cerium nitrate.

Next, Ti is evaporated with a thickness of 50 nm by sputtering scheme.

And then, unnecessary Ti and resist are exfoliated at the same time(lift-off scheme) (FIG. 5B).

(Step 3)

A complex solution, in which isopropyl alcohol and so on is applied toPd complex, is entirely applied to the substrate by spin coating.

After application, a heating operation is performed at 300° C. in anatmosphere. Palladium oxide 51 is formed with a thickness of about 10nm, and then, remaining Cr is all removed by an etching solution made ofmade of cerium nitrate.

At this moment, the surface of the undercoating Ti layer 5 is oxidized.A sheet resistance of the layer 5 is 1×10² Ω/□ and conductivity isobtained (FIG. 5C).

(Step 4)

After evacuation of atmosphere, the substrate 1 is heated at 200° C. andis heated in 2%-hydrogen airflow, which is diluted with nitrogen. Inthis step, particles 52 each having a diameter of about 3 to 10 nm areformed on the surface of the device. At this moment, a density ofparticles is estimated at 10¹¹ to 10¹²/cm² (FIG. 5D).

(Step 5)

Subsequently, a heating operation is performed in 0.1%-ethylene airflow,which is diluted with nitrogen, at 500° C. for 10 minutes to formfibrous carbon.

When the electron-emitting device obtained in the above manufacturingsteps was observed by a scanning electron microscope, it was found thatmuch fibrous carbon was formed on the Pd applying region while bendingand spreading in a fibrous form with a diameter of about 10 to 25 nm. Atthis moment, fibrous carbon was about 500 nm in thickness (FIG. 5E).

Additionally, in the figures, catalyst particles were disposed onpositions making contact with a conductive material. Catalyst particlessometimes existed on the end of the fibrous carbon or a midpoint offiber.

In order to study electron-emitting efficiency of the above device, thedevice was disposed in the vacuum apparatus 60 shown in FIG. 6, and thevacuum evacuating apparatus 65 sufficiently performed evacuation until2×10⁻⁵ Pa. And then, a voltage of Va=10 kV was applied to the positivepole (anode) 61, which was away from the device by H=2 mm, as a positiveelectrode (anode) voltage. Further, a pulse voltage including a drivingvoltage of Vf=20 V was applied to the device and measurement was made ona device current If and an electron emission current Ie that wereapplied at this moment.

The device had Ie characteristics shown in FIG. 7. To be specific, Ierose sharply from about a half of applied voltage, and when Vf was 15 V,an electron emission current Ie of about 1 μA was measured. Meanwhile,If (not shown) was similar to Ie in characteristics and an If value wassmaller than Ie by an order of magnitude.

As described above, the layer 5 having growth selectivity of fibrouscarbon was formed on the cathode electrode 3 in the present example.Thus, it was possible to grow fibrous carbon at a predetermined positionwith a fixed high density.

Moreover, since the layer 5 was used as an electrical connecting layerbetween fibrous carbon and the electrode 3, it was possible to obtainelectrical connection with stability between the fibrous carbon and theelectrode 3 and to emit electrons in a stable manner.

In the present example, partially oxidized Ti or an oxide semiconductormade of Ti was used as a material of the layer 5. Instead of Ti, it ispossible to adopt Zr, Nb, or Al. Further, even in the case of a materialother than these, it is preferably used with growth selectivity offibrous carbon.

In the present example, after the cathode electrode 3 is formed in Step1, the layer 5 was stacked on the cathode electrode 3. The cathodeelectrode 3 and the layer 5 may be formed at the same time by using thesame material. At this moment, since the material having growthselectivity of fiber carbon is used as a material, it is possible toform the electron-emitting device with a simpler process.

Beam obtained by the electron-emitting device of the present example wassubstantially rectangular with a length in Y direction and a width in Xdirection.

A driving voltage Vf was fixed at 15 V, and a distance H between anodeswas fixed at 2 mm. A beam width was measured as shown in Table 1 inwhich an anode voltage was set at 5 kV and 10 kV and a gap was set at 1μm and 5 μm.

TABLE 1 Va = 5 kV Va = 10 kV Gap: 1 μm X direction:  60 μm X direction: 30 μm Y direction: 170 μm Y direction: 150 μm Gap: 5 μm X direction: 93 μm X direction:  72 μm Y direction: 170 μm Y direction: 150 μm

Besides, an electric field required for driving could be changed byvarying the conditions of growing fibrous carbon. Particularly anaverage particle diameter of Pd, which is formed by reducing palladiumoxide, was associated with a diameter of fibrous carbon formedthereafter. It was possible to control an average diameter of Pd by a Pdconcentration of a Pd complex and the number of revolutions of spincoating.

When fibrous carbon of the device is observed by a transmission electronmicroscope, as shown in the right of FIG. 12, graphen was stacked alongan axial direction of fibrous carbon. A stacking interval of graphen (ina direction of Z axis) is unclear at a low temperature of about 500° C.and an interval was 0.4 nm. An interval of grid became clear withtemperature. An interval was 0.34 nm at 700° C., which is close to 0.335nm of graphite.

Example 2

FIGS. 2A and 2B show Example 2.

In the present example, an electron-emitting device was manufactured inthe same manner as Example 1 except that the cathode electrode 3 b was500 nm in thickness and the extracting electrode 2 was 30 nm inthickness, and measurement was made on If and Ie.

Other configurations and effects are the same as those of Example 1.Hence, the same members will be indicated by the same reference numeralsand the description thereof is omitted.

In the device configuration of the present example, a position foremitting electrons was positively set at a high position (anode side)from the extracting electrode 2 by increasing a thickness of the cathodeelectrode 3 b.

With this configuration, since trajectories of electrodes colliding withthe gate were reduced, it was possible to prevent a reduction inefficiency and an increase in beam diameter.

Consequently, in the present device configuration as well, an electronemission current Ie of about 1 μA was measured when Vf was 20 V.Meanwhile, If was similar to Ie in characteristics. A value of If wassmaller than Ie by two digits.

Besides, a beam diameter at this moment was substantially equal to thatof Table 1.

Example 3

FIGS. 3A and 3B show Example 3.

In the above example, the layer 5 and the electron-emitting member 4 areformed on the cathode electrode 3. In the present example, a layer 5 cand an electron-emitting member 4 c are formed across the cathodeelectrode 3 and a gap (space) between the cathode electrode 3 and thegate electrode 2.

In the step 2 of Example 1, a resist pattern is formed in the same stepas Example 1 except that a position for forming a resist pattern ischanged. Thus, the description thereof is omitted.

Besides, in the present example, the layer 5 c and the electron-emittingmember 4 c are extended to an about intermediate point (about a half ofa distance between the gaps) of a gap between the cathode electrode 3and the gate electrode 2 such that a distance is small between theelectron-emitting member 4 c and a extracting electrode 2.

This device has an electric field about twice as large as that of thedevice of Example 1 since its distance between the gaps is smaller thanthat of Example 1. Accordingly, the driving voltage can be reduced toabout 8 V.

Further, since the layer 5 is used as an electrical connecting layer offibrous carbon, it was possible to emit electrons with stability fromfibrous carbon in a gap.

Example 4

FIGS. 4A and 4B show Example 4.

In the present example, Steps 1 and 2 of Example 1 were changed asfollows.

(Step 1)

A quartz substrate is used as the substrate 1. After sufficientcleaning, Ti having a thickness of 5 nm and Pt having a thickness of 30nm are evaporated continuously as a cathode electrode 3 d by sputteringscheme, and Ti having a thickness of 100 nm is continuously evaporatedas a layer 5 d being capable of growing fibrous carbon.

Next, in a photolithography process, a resist pattern is formed using apositive photoresist (AZ1500/manufactured by Clariant InternationalLtd.).

Next, dry etching is performed on the Ti layer (layer 5 d) using CF₄with the patterned photoresist serving as a mask, and then, dry etchingis performed on the Pt and Ti layers (cathode electrode 3 d) by using Arto form the cathode electrode 3 d.

Subsequently, with the cathode electrode 3 d serving as a mask, etchingis performed on a quartz substrate at a depth of about 500 nm by usingmixed acid composed of hydrogen fluoride and ammonium fluoride.

And then, Ti having a thickness of 5 nm and Pt having a thickness of 30nm are evaporated continuously as the extracting electrode 2 d bysputtering scheme again. After a photoresist of the cathode electrode 3d is exfoliated, a resist pattern for forming the lead electrode patternby using a positive photoresist (AZ1500/manufactured by ClariantInternational Ltd.) again.

Then, dry etching is performed on the Pt layer and Ti layer using Ar gaswith the patterned photoresist serving as a mask to form the extractingelectrode 2 so as to allow the step formed between the electrodes toserve as a gap.

The steps thereafter are substantially the same as those of Example 1.

However, in the present example, Ni was used as a catalyst material forgrowing fibrous carbon. At this moment, the resist pattern is formed onthe conductive layer 5 d, and Ni particles are formed with a thicknessof about 5 nm by resistance heating evaporation having good linearlity.And then, oxidization is preferably performed at 350° C. for 30 minutes.

In the present example, since the substrate 1 d had a step height tomake a height difference between the electrodes, it was possible to forma finer gap and to emit electrons from about 6 V.

Further, because the electrode material 4 d was high (large thickness),electrons can be emitted from an intermediate point as well as an upperpart of the film. Hence, it was possible to prevent electrons fromcolliding with the extracting electrode 2 d to reduce efficiency andincrease a beam diameter.

Example 5

Referring to FIGS. 8, 9, and 10, the following will discuss animage-forming apparatus in which a plurality of electron-emittingdevices is arranged according to an embodiment of the present invention.In FIG. 8, reference numeral 81 denotes an electron source substrate,reference numeral 82 denotes X-direction wiring, and reference numeral83 denotes Y-direction wiring. Reference numeral 84 denoteselectron-emitting devices and reference numeral 85 denotes connection.

When a capacity of the device increases because a plurality of theelectron-emitting devices 84 is provided, in matrix wiring of FIG. 8,even if a short pulse is applied due to pulse width modulation, acapacity component forms bluntness on a waveform and desired gradationcannot be obtained. Therefore, the present example adopts aconfiguration in which an interlayer insulating layer is disposeddirectly beside an electron-emitting member to suppress an increase incapacitivity on a part other than the electron-emitting member.

In FIG. 8, the X-direction wiring 82 is composed of m wires of Dx1, Dx2,. . . , and Dxm and is made of an aluminum wiring material with athickness of about 1 μm and a width of 300 μm by a scheme such asevaporation. A material, a thickness, and a width of wiring are set asappropriate.

The Y-direction wiring 83 is composed of n wires of Dy1, Dy2, . . . ,and Dyn having a thickness of 0.5 μm and a width of 100 μm which areformed in the same manner as the X-direction wiring 82.

Between the X-direction wiring 82 having m wires and the Y-directionwiring 83 having n wires, an interlayer insulting film (not shown) isprovided to electrically insulate the wiring (m and n are both positiveintegers).

The interlayer insulating film (not shown) is made of a material such asSiO₂, which is formed with a thickness of about 0.8 μm by a scheme suchas sputtering scheme. The interlayer insulating film is formed entirelyor partially on the electron source substrate 81 having the X-directionwiring 82 formed thereon with a predetermined pattern. Particularly afilm thickness is determined to be resistant to a potential differenceon the intersection of the X-direction wiring 82 and the Y-directionwiring 83. In the present example, a thickness of the interlayerinsulating film is determined such that each device has a devicecapacity of 1 pF or lower and a device resistance of 30 V.

The X-direction wiring 82 and the Y-direction wiring 83 are each drawnas external terminals.

A pair of electrodes (not shown) constituting the electron-emittingdevice 84 is electrically connected to the m wires of the X-directionwiring 82 and the n wires of the Y-direction wiring 83 via theconnection 85 made of a material such as conductive metal.

Scanning signal applying means (not shown), which applies a scanningsignal for selecting a row of the electron-emitting devices 84 arrangedin X direction, is connected to X-direction wiring 82. Meanwhile,modulating signal generating means (not shown) for modulating eachcolumn of electron-emitting devices 84 in response to an input signal isconnected to the Y-direction wiring 83. A driving voltage applied toeach of the electron-emitting devices is supplied as a differencevoltage between a scanning signal and a modulating signal. Thedifference voltage is applied to the device.

In the present example, connection is made such that the Y-directionwiring 83 has a high potential and the X-direction wiring 82 has a lowpotential. Such connection achieves the converging effect of beam.

In the above configuration, with passive matrix wiring, it is possibleto select each of the devices and drive them in isolation from eachother.

Referring to FIG. 9, the following will discuss an image-formingapparatus constituted by an electron source using a passive-matrixelectron source.

FIG. 9 is a schematic perspective view showing a display panel of theimage-forming apparatus using soda lime glass as a glass substratematerial.

In FIG. 9, reference numeral 81 denotes an electron source substrate,reference numeral 91 denotes a rear plate on which the electron sourcesubstrate 81 is fixed, reference numeral 96 denotes a face plate havinga fluorescent film 94, a metal back 95, and so on formed on an innersurface of a glass substrate 93. Reference numeral 92 denotes a supportframe having the rear plate 91 and the face plate 96 connected theretoby using frit glass and the like. Reference numeral 97 denotes asurrounding member which is sealed by firing for 10 minutes or more at atemperature range of 450° C. in a vacuum.

As described above, the surrounding member 97 is composed of the faceplate 96, the support frame 92, and the rear plate 91. Further, it ispossible to form the surrounding member 97 with sufficient strength toan air pressure by providing a support (not shown) referred to as aspacer between the face plate 96 and the rear plate 91.

The metal back 95 is formed as follows: after the fluorescent film 94 isproduced, a smoothing operation (normally referred to as “filming”) isperformed on an inner surface of the fluorescent film 94, and then, Alis deposited by a scheme such as vacuum evaporation.

The face plate 96 has a transparent electrode (not shown) on theexterior of the fluorescent film 94 to further increase conductivity ofthe fluorescent film 94.

When the above sealing is made, the phosphors and the electron-emittingdevices need to correspond to each other in the case of a color display,and sufficient positioning is necessary.

In the present example, since electrons from the electron source areemitted to the gate electrode, when an anode voltage is 10 kV and adistance between anodes is 2 mm, the phosphors are shifted to the gateonly by 200 μm.

FIG. 10 is a schematic diagram showing a circuit configuration of theimage-forming apparatus of the present example.

A scanning circuit 102 has M switching elements (schematically indicatedby S1 to Sm in FIG. 10) therein. The switching elements each select anoutput voltage of a DC voltage source Vx or 0 V (ground level) and areelectrically connected to terminals Dox1 to Doxm of a display panel 101.

The switching elements S1 to Sm are operated in response to a controlsignal T_(scan), which is outputted by a control circuit 103. Forexample, a switching element such as an FET is combined to constitutethe switching elements.

The DC voltage source Vx is set to output a constant voltage such that adriving voltage applied to a device not being scanned is at or lowerthan a electron-emitting threshold voltage, based on the characteristics(electron-emitting threshold voltage) of the electron-emitting device.

The control circuit 103 has the function of matching the operations ofthe members so as to provide suitable display in response to an imagesignal inputted from the outside. The control circuit 103 producescontrol signals T_(scan), T_(SFT) and T_(MRY) for each of the membersbased on the synchronization signal T_(SYNC) transmitted from thesynchronization signal separating circuit 106.

A synchronization signal separating circuit 106 is provided forseparating a synchronization signal component and a luminance signalcomponent from a television signal of NTSC scheme that is inputted fromthe outside, and the synchronization signal separating circuit 106 iscomposed of a typical frequency separating (filter) circuit and so on. Asynchronization signal separated by the synchronization separatingcircuit 106 includes a vertical synchronization signal and a horizontalsynchronization signal and is indicated by T_(SYNC) signal forconvenience of explanation. The luminance component of the image that isseparated from the television signal is indicated by DATA signal forconvenience. The DATA signal is inputted to a shift register 104.

The shift register 104 is provided for carry out serial/parallelconversion on the DATA signal, which is inputted to the serial on thetime series, for each line of the image, and the shift register 104 isoperated in response to a control signal TSFT transmitted from thecontrol circuit 103 (namely, the control signal TSFT also serves as ashift clock of the shift resistor 104). Data subjected toserial/parallel conversion for each image line (corresponding to drivingdata of N electron-emitting devices) is outputted from the shiftregister 104 as N parallel signals of Id1 to Idn.

The line memory 105 is a memory for storing data for each image line fornecessary time and stores the contents of the Id1 to Idn if necessary inresponse to a control signal T_(MRY) transmitted from the controlcircuit 103. The stored contents are outputted as Id′1 to Id′n and areinputted to a modulation signal generator 107.

The modulation signal generator 107 is a signal source for suitablycarry out driving modulation on the electron-emitting devices accordingto the image data Id′1 to Id′n. The output signal is applied to theelectron-emitting device in the display panel 101 through the terminalsDoy1 to Doyn.

As described above, the electron-emitting device according to theembodiment of the present invention has the following fundamentalcharacteristics relative to an emission current Ie.

Namely, emission of electrons has a definite threshold voltage Vth.Electrons are emitted only when a voltage at Vth or higher is applied.As for a voltage at an electron-emitting threshold value or higher, anemitting voltage varies according to a change in voltage applied to thedevice.

Therefore, when a pulse voltage is applied to the device, for example,even when a voltage at or lower than an electron-emitting thresholdvalue is applied, electrons are not emitted. However, when a voltage ator higher than an electron-emitting threshold value, electron beam isoutputted.

At this moment, it is possible to control the intensity of electron beamby changing a peak value Vm of pulse. Further, it is possible to controla total amount of charge of electron beam, which is outputted bychanging a pulse width Pw.

Accordingly, a voltage modulating scheme, a pulse width modulatingscheme, and so on are applicable as a scheme for modulating theelectron-emitting device.

When the voltage modulating scheme is carried out, as the modulationsignal generator 107, it is possible to adopt a circuit of the voltagemodulating scheme that generates a voltage pulse with a fixed length andmodulates a peak value of pulse in response to inputted data.

When the pulse width modulating scheme is carried out, as the modulationsignal generator 107, it is possible to adopt a circuit of the pulsewidth modulating scheme that generates a voltage pulse with a fixed peakvalue and modulates a pulse width in response to inputted data.

Digital signal scheme is used for the shift register 104 and the linememory 105.

In the present example, a circuit such as a D/A conversion circuit isused for the modulation signal generator 107, and an amplifying circuitis additionally provided if necessary. In the case of the pulse widthmodulating scheme, as for the modulation signal generator 107, a circuitis used in which a counter and a comparator are combined with eachother. The counter is provided for counting the number of wavesoutputted from a high-speed oscillator and an oscillator, and thecomparator is provided for comparing an output value of the counter andan output value of the memory.

The above-mentioned configuration of the image-forming apparatus is anexample of the image-forming apparatus in which the present invention isapplicable. A variety of variations are allowed based on the technicalidea of the present invention. Although the NTSC system was describedfor an input signal, an input signal is not limited to the NTSC system.It is possible to adopt PAL, SCAM, and a TV signal (e.g., ahigh-definition TV such as MUSE system) system using a larger number ofscanning lines.

As described above, the present invention is provided with a conductivelayer for growth selectivity of fibrous carbon. It was possible to makeelectrical connection with stability by growing fibrous carbon at apredetermined position with a high density, to reduce a device capacityand a driving voltage and improve the efficiency of emitting electrons,and to achieve a high-resolution beam.

1. An electron-emitting device comprising: (A) a plurality of fiberseach comprising carbon; and (B) a layer made of an oxygen-deficient typemetal-oxide semiconductor, wherein metal-oxide of the oxygen-deficienttype metal-oxide semiconductor is selected from the group consisting oftitanium oxide, zirconium oxide, and niobium oxide, wherein the fibersare electrically connected with the layer.
 2. An image-forming apparatuscomprising a plurality of electron-emitting devices and a light-emittingmember which emits light by irradiation of electrons emitted from aplurality of electron-emitting devices, wherein each of theelectron-emitting device is an electron emitting device according toclaim 1.